In the chemical, petroleum, metallurgical or electrical industries, etc., the high temperature dust-containing gas is normally produced, and has to be deashed since it is necessary for different processes to recycle the energy and meet the emission standards for environment preservation. Deashing the high-temperature gas is a technique to accomplish the gas purification through directly separating the gas and solid, which can increase the rate of energy utilization by utilizing the physical sensible heat, chemical latent heat and kinetic force of the gas to the greatest extent, as well as can simplify the processing and save the equipment investment.
The rigid high-temperature filtration elements such as the sintered metal filtration pipeline and ceramic filter tube, etc. possess good performances in anti-seismic, the high-temperature resistance, the corrosion resistance and thermal impact, as well as comparatively high filtration accuracy and efficiency. Therefore, they are broadly applied in the field of purifying the high-temperature gas.
When the high-temperature dust-containing gas enters into the filter, the dust particles in the airflow are intercepted and form a filtration cake layer on the outside surface of the filtration element, and the gas passes through the porous passages of the filtration element for the followed-up processes. The filtered gas becomes clean and contains dust with very low density. With the continuous filtering, the dust cake layer on the outside surface of the filtration element gradually becomes thick, which results an increase in the pressure drop of the filtration element and requires the application of back-flushing to reactivate the performance and function of the filtration elements. With the direction opposite to the filtration flow, the high-temperature back-flushing airflow enters into the inner side of the filtration element instantaneously to generate the momentary energy to peel off the dust cake layer attached on the outside surface of the filtration element, with the pressure drop of the filtration element restoring to the pressure for the primary filtration, and therefore the performance and function of the filtration element is reactivated.
The pulse-jet cleaning method is an important method for realizing the recycle and reactivation of the performance and function of the filtration element. The deashing performance of a pulse jet cleaning device decides whether the high-temperature gas filter can stably operate in a long term or not.
The high-temperature gas filter mainly has two kinds of structures, a circular structure and a square structure (depending on the shapes of the tube sheets). FIGS. 9A and 9B schematically show the structure of a high-temperature filter 800 with the circular structure, which is mainly used in the operating conditions with high temperature and high pressure (the parameters for the typical working situation: the operating pressure is about 4-6 MPa and the operating temperature is about 350-450° C.). FIGS. 10A and 10B schematically show a structure of a high-temperature filter 900 with the square structure, which is mainly used in the operating conditions with high temperature and low pressure (the parameters of the typical working situation: the operating pressure is about 0.2-0.4 MPa, and the operating temperature is about 550-650° C.). The two high-temperature filters in different structures have the same operating principles.
As shown in FIGS. 9A, 9B, 10A and 10B, the tube sheet 803 and 903 of the filter 800 and 900 divide the filter into two portions with the lower portion called the dust-containing gas side and the upper portion called the cleaning gas side. The dust-containing gas (or coarse mixed gas) enters into the dust-containing gas side of the filter through the gas inlets 801 and 901 of the filters 800 and 900, and arrives at each filtration unit by the impetus of the gas, the dust particles in the gas being intercepted and forming the dust cake layer on the outside surface of the filtration pipeline 802 and 902, and the gas entering into the cleaning gas side after being filtered through the porous passages of the filtration pipeline 802 and 902, and being discharged through the gas outlet 805 and 905 for the followed-up processes. With the continuous filtering, the dust cake layer on the outside surface of the filtration pipeline 802 and 902 gradually becomes thick, which results an increase in the pressure drop of the filter 800 and 900 and requires the application of back-flushing to reactivate the performance and function of the filtration elements. During the pulse-jet cleaning, with the normally closed pulse back-flushing valves 808 and 908 being open, the high pressure nitrogen or clear mixed gas in gas tank 809 and 909 enters into the back-flushing pipeline 807 and 907 instantaneously and ejects the back-flushing gas in the high pressure and high speed to the inside of the corresponding ejectors 804 and 904 through the nozzle 806 and 906 on the tube, and then the back-flushing gas enters into the inner side of the corresponding filtration pipelines 802 and 902 to generate the momentary energy to peel off the dust cake on the outside surface of the filtration pipelines 802 and 902 and make the resistance of the filtration pipeline basically restore to the initial level, so as to realize the reactivation of the performance and function of the filtration pipeline.
As shown in FIGS. 9A and 9B, in the case that the filter 800 has the filtration pipelines arranged in a circular shape, each filtration unit is provided with a plurality of (normally 48) filtration pipelines therein and all filtration units share one ejector 804, wherein in the circular filtration unit, the filtration pipelines 802 are arranged in the congruent triangle shape, 12 or 24 filtration units normally are provided on the tube sheet 803 of the filter. When performing the back-flushing, based on the previously set back-flushing time, the first group of the filtration units is back flushed, and after a period of time, the second group of filtration units is back flushed, and then after another period of time, the third group of filtration units is back flushed. The process is repeated in cycle.
As shown in FIGS. 10A and 10B, in the case that the filter 900 has the filtration pipelines arranged in a square shape, the filtration pipelines 902 are arranged on the tube sheet 903 with the equal distance among the rows and lines, and divided into several groups in the unit of lines, normally several or more than 10 filtration pipelines 902 being provided in each line with the filtration pipelines 902 in each line corresponding to one ejecting and flushing tube 907, several nozzles 906 being provided on each ejecting and flushing tube 907, and a filtration pipeline 902 being provided right under each nozzle 906. The back-flushing is performed group by group in the unit of lines, namely, the pulse back-flushing valve 908 for the first line of filtration pipelines opens and the corresponding ejecting and flushing tube 907 back flushes the line of filtration elements, after a period of time, the pulse back-flushing valve 908 for the second line of filtration pipelines opens and the corresponding ejecting and flushing tube 907 back flushes the second line of filtration elements, and then after another period of time, the pulse back-flushing valve 908 for the third line of filtration pipelines opens and the third line of filtration elements are back flushed. The process is repeated in cycle.
To sum up, the pulse back-flushing of the high-temperature gas filter in the prior art achieves the deashing effect mainly through the momentary energy by causing a high-pressure back flushed gas to generate a pressure wave in the filtration pipeline. In the prior art, the nozzle of the pulse back-flushing device is in a normal single hole structure (single tube) and provided on the back-flushing pipeline, which causes the pressure wave to be generated in the filtration pipeline only one time when the back flushed gas is ejected through the nozzle in such structure. Normally, the higher the pressure of the back-flushing is, the higher the peak value of the generated pressure is and the better the deashing effect is. But in the practical operation, the back-flushing in the prior art will unavoidably cause the following problems.
(1) Over High Pressure of the Pulse-Jet Cleaning
Due to that the back-flushing gas needs to overcome the operating pressure of the filter and the flowing resistance of the filtered gas flow, the energy of the back-flushing gas cannot be completely applied on the filtration unit. Therefore, the deashing pressure over 2 times than the filter operating pressure in the practical operation is needed, and the back-flushing pressure under the high-temperature and high-pressure working situation will reach at 8 PMa, which causes a great impact on the filter tubes and easily causes the filtration pipeline vibrate. The higher pressure is, and the more seriously the filtration pipeline vibrates. Such high pressure deashing operation can easily cause breakage and even fracture of the filtration pipeline due to the thermal impact fatigue.
(2) Non-Uniformity of Pulse-Jet Cleaning Effects
During the pulse-jet cleaning, the back flushed flow will continuously leak from the gaps among the porous passages when the momentary energy generated by the back flushed flow enters into the filtration pipeline and is transmitted from the opening end of the filtration pipeline to the sealed end, which causes the continuous dissipation of the energy during the transmission and great difference of the deashing effects from the lower portion of the filtration pipeline to the upper portion of the filtration pipeline, with the dust cake attached on the surface of the lower portion of the filtration pipeline being uneasily cleaned by the back flushed flow and thereby occurring the incomplete deashing phenomenon, which causes the bridging of the dust cakes among the filtration pipeline and the malfunction of filtration pipeline as a consequence.
(3) Low Efficiency of Pulse Jet Cleaning
As stated above, the back-flushing techniques in the prior art evaluate the deashing effect mainly by the pressure peak of the back-flushing, wherein the pressure peak value refers to the biggest pressure generated by the ejected deashing flow from the back-flushing device in the filtration pipeline at the moment of pulse ejecting. However, the high pressure peak value may not achieve the ideal deashing effect, mainly because each time that the back-flushing by the pulse-jet cleaning device (i.e. the pulse back-flushing valve opens one time), the pressure wave can only be generated in the filtration pipeline one time. As the deashing effect on the upper position of the filtration pipeline is greatly different from that on the lower position and the energy of the generated pressure wave decreases quickly, the efficiency of pulse-jet cleaning in the actual operation of the high-temperature filter is relatively low, which cannot achieve the ideal deashing effect.
It seems that the regeneration efficiency can also be improved if the pulse back-flushing solenoid valve is opened and closed more times during the deashing, in the case that the pulse-jet cleaning device in the prior art is used, each time the pulse back-flushing solenoid valve being opened, the filtration pipeline being deashed one time. However, such operation is inapplicable for the following reasons: first, the pulse back-flushing solenoid valve is expensive with the membrane of the solenoid valve having a limited service life, and the repetitive activation of the solenoid valve will also reduce the service life; second, the filtered dust-containing gases under the high-temperature operating situation mainly contain the corrosive, inflammable and explosive gas, which requires the purified intert gas (such as nitrogen) as the deashing gas resource for deashing. However, the cost of the intert gases is high, and repetitive activation of the solenoid valve will also increase the consumption of the back-flushing gas; third, due to the relatively high back-flushing pressure required by the pulse back-flushing, a big thermal impact on the filtration pipeline is generated when the back-flushing flow enters into the filtration pipelines. It is certain that the repetitive activation of the pulse back-flushing solenoid valve will destroy the filter tube and shorten the service life of the tubes; four, an important principle of pulse jet cleaning is that the deashing can only be performed when the dust cake on the outside surface of the filtration pipeline becomes thick to a certain extent. Otherwise, the weak interacting force among the dust cakes due to the thinness of the dust cake, results in that the deashing energy is ineffective and thereby the thin dust cake cannot be peeled off. Therefore, although the back-flushing effect does not reach the requirement, the solenoid valve cannot be activated to deash, and only when the dust cake on the surface of the filtration pipelines is accumulated in a certain thickness, can the back-flushing be executed again.
Therefore, the inventor himself proposes a self-oscillating nozzle and a pulse-jet cleaning device with the self-oscillating nozzle to overcome such technical defects, based on years of experience and practice in working in the related industry.